The present invention comprises a new variety of sand cherry, or dwarf cherry (Prunus pumila), referred to by the varietal name `Rhenus 2`. `Rhenus 2` is useful, for example, as a rootstock for peach, nectarine, apricot, and other Prunus varieties, displaying good compatibility and producing dwarf trees with high yield efficiency and high frost hardiness, thus allowing such varieties to be grown in colder climates.
The new variety was selected by me in a cultivated area in an orchard at the Research Station of Viticulture and Horticulture in Geisenheim, Germany. At the Research Station, fifty-five Prunus pumila seedlings resulting from open pollination of a Prunus pumila maternal parent were selected for testing. Five peach varieties (`Sunglo`, `Sunking`, `Red Haven`, `Fair Haven`, and `Hale Berta Giant`) were grafted to rootstock of these seedlings and to the rootstock `Nemaguard` for comparison purposes. Fifteen trees of each of the grafted varieties were observed from 1986 to 1995 with regard to the following parameters: trunk cross-sectional area, cumulative marketable yield, yield efficiency, blossoming (from 1987 to 1995), tree health, compatibility, frost hardiness, suckering, soil adaptation. Clone 73/95 was one of the seedling clones with the best results.
In 1994, a second trial was performed. Thirty trees from each of four peach varieties (`Suncrest`, `Early Red Haven`, `Hale Berta Giant`, and `Redcal`) and seventeen trees from each of three apricot varieties (`Orangered`, `Hargrand`, and `Harlayne`) were grafted to rootstock from selected Prunus pumila seedlings from the first evaluation and to `Nemaguard` rootstock for comparison purposes. Clone 73/95 displayed the best results of the seedlings tested and was renamed `Rhenus 2`.
`Rhenus 2` has not been observed under all possible environmental conditions and its phenotype may vary significantly with variations in environment such as temperature, light intensity, and daylength, without any variation in genotype. Howerver, the following unique combination of characteristics have been repeatedly observed in asexually propagated progeny of `Rhenus 2` and distinguish it from all other varieties: (1) causes substantial dwarfing when used as a rootstock for peach, nectarine, and apricot scions with no significant reduction in fruit size; (2) compatibility as a rootstock with a wide variety of peach, nectarine, and apricot varieties; (3) when used as a rootstock, provides an early yield, high yield efficiency, substantially uniform fruit size, high frost hardiness, no suckering, and good soil adaptation. These characteristics are established and transmitted through succeeding asexual propagations.
Asexual reproduction of `Rhenus 2` was performed by hardwood cuttings, softwood cuttings (e.g., tips and intermediate cuttings), stool bed propagation (layering), and tissue culture. Asexual propagation has been accomplished in McMinnville, Oreg. and elsewhere in Germany. Other conventional methods for propagation of Prunus pumila varieties may also be used. Best results have been observed with hardwood cuttings (quick dipping using 4000 ppm indole-3-butyric acid [IBA]).